It has been the universal commercial practice to pass a rope slowly through a bath of liquid material to permit the material to penetrate the voids or interstices of the rope. Such a method and a device for carrying out the method are known from U.S. Pat. No. 3,960,050 wherein the rope is placed in a basket which is immersed in an impregnation tank containing the liquid material to be impregnated in the rope. Alternatively, the rope may be passed through an impregnation bath containing said liquid. U.S. Pat. No. 3,960,050 also describes a device for carrying out the method disclosed therein. Further methods for impregnating a rope and devices for carrying out said methods are known from U.S. Pat. No. 4,197,695 wherein an impregnation bath or an impregnation closing die are used; U.S. Pat. No. 4,490,969 wherein an impregnation bath or a spraying device are used; U.S. Pat. No. 5,098,493 wherein injection needles are used; and U.S. Pat. No. 4,635,432 wherein an injection die is used.
Another device for impregnation is disclosed for example in U.S. Pat. No. 1,587,652 which is used to saturate a fibrous material in particular a felt sheet with e.g. asphalt. The device disclosed therein contains a pressure saturating chamber which uses high pressure, i.e. pressure higher than the atmospheric pressure, to cause the asphalt to penetrate the sheet. After saturating or impregnating the sheet using high pressure, the device may subsequently use vacuum to extract any moisture or air trapped therein; and then the sheet may be again subjected to saturation under great pressure. Vacuum however is not used during the saturation step.
CA 768356 also discloses a device for impregnating a textile, the device comprising an impregnation bath containing an impregnant and a vacuumed column located within the impregnant such that the impregnant acts as a seal for the bottom of the column. Just as in U.S. Pat. No. 1,587,652, vacuum is used to extract any air which may be retained within the impregnated textile. A device similar to the one of CA 768356 is disclosed by JP 48-41094.
Another disclosure of a device for impregnating a wire rope is given by JP 2005 264358. The device disclosed therein operates in a batch-like fashion wherein a portion of a length of the wire rope is placed in a vacuumed tube and a molten resin is injected under pressure in said tube, to impregnate said portion. After impregnation, the vacuum is released, the impregnated portion of the rope is removed from the tube and a portion of the adjacent non-impregnated part of the rope is placed in the tube. The operation is repeated to impregnate the complete length of the rope.
Moreover, although impregnating a rope and coating a rope are in principle two different processes with different characteristics, in some instances is arguable that the methods for coating a rope may also achieve some low degree of impregnation. A method for coating a rope is described for example in JP 5 510 2457, wherein the rope is coated with grease by injecting the grease into a chamber while the chamber moves along the length of the rope. The thickness of coated grease is controlled by the size of the gap between the outer periphery of the rope and the internal periphery of the outlet of the chamber which discharges the rope. Further methods for coating ropes wherein some degree of impregnation may be achieved are known from U.S. Pat. No. 4,067,211 wherein a spraying method is used for coating the rope; and U.S. Pat. No. 8,105,657 wherein a coating chamber is used.
It was however noticed that the results obtained with the known impregnation or coating methods may depend on the modus operandi, or in other words, to the skills of the operator, i.e. the person carrying out the method. The rather poor reproducibility of such methods typically implies that the quality of the impregnation may vary with the skills of the operator and in turn, impregnated ropes forming for example a rope batch may have inconsistent properties. Also due to the employment of complicated machinery and/or heavy hardware, the known methods may be cumbersome to use and even pose safety risks.
It was also noticed that the above mentioned methods have difficulties in achieving an optimum degree of impregnation; in particular since the liquid material does not always optimally penetrate inside the rope. Moreover, achieving sizeable rope lengths which are optimally impregnated with the liquid material along a significant, preferably entire, length thereof is hardly possible. Especially for thick ropes, e.g. ropes having an effective diameter of more than 10 mm and even more than 20 mm, it was observed that the liquid material hardly penetrates fully the rope reaching the core of the rope also. Such an uneven distribution of the liquid material inside the rope may in turn cause a reduced life time thereof and even variations in rope strength along its length during its use.
To partly solve the above drawbacks and in particular the inhomogeneous penetration, methods were devised where ropes were assembled from previously coated fibers or coated strands containing fibers. Such a method is for example disclosed in DE 749 220. Therein, before constructing a rope, the individual elements of the rope, e.g. fibers, yarns of strands, are coated or impregnated by passing several filaments through an impregnation bath and thereafter combining them in an elongated nozzle tube. However, processes such as the one of DE 749 220 are very complicated and extremely polluting. Also, it came as a surprise for such methods that in spite of distributing a liquid material on each fiber or strand of the rope, the exterior of the rope assembled from said fibers and/or strands contained less liquid material than the core of the rope. Hence, even for such methods the degree of rope impregnation can be optimized.
Accordingly, the object of the present invention may be to provide a method for coating a rope which shows the above mentioned disadvantages to a lesser extent. In particular, the present invention aims to provide a method for more uniformly impregnating a rope with a liquid material and a device for carrying out said method.